TWiki

FAQ:

What happens if two of us try to edit the same topic simultaneously?

Answer:

The second person gets a warning that the topic is currently being edited by another user. A topic gets locked automatically for some time (default is one hour) when you edit, preview or save the topic. If you get the lock warning you should wait until the lock is gone or contact the other person to ask if you can go ahead and break the lock. See also UnlockTopic.